A reduction in the size of pigment particles so as to improve its spectral characteristics, such as tinting strength and transparency, results in an increase in the growth or transformation of crystals caused by thermal history or contact with a solvent in a dispersion process and subsequent processes, resulting in a decrease in the tinting strength and transparency of the pigment.
Various pigment compositions and pigment dispersants have been proposed in order to improve the dispersibility of pigments. PTL 1 discloses the use of a comb polymer dispersant having an acidic or basic portion known as Solsperse (registered trademark). PTL 2 discloses the use of a polymer dispersant for an azo pigment in an ink jet recording method. The polymer dispersant is a water-soluble polymer having a chromophore bonded to its side chain or end. The chromophore has a molecular weight of less than 95% of the molecular weight of the azo pigment.
PTL 3 discloses the use of a mixture of at least two organic pigments in red (R), green (G), and blue (B) color filters in order to achieve desired color characteristics. Particularly in the case of the green color filter, a main pigment, a copper phthalocyanine green pigment, is combined with an azo yellow pigment for tone adjustment.
However, the pigment dispersant described in PTL 1 cannot sufficiently disperse an azo pigment because of insufficient affinity for the azo pigment. The pigment dispersant described in PTL 2 is a water-soluble polymer and therefore results in poor dispersion in a system using a water-insoluble solvent as a dispersion medium.
There has been a problem that the use of an azo pigment in a color filter resist results in poor and unstable pigment dispersion and consequently poor color characteristics of the color filter.